A grain oriented electrical steel sheet is mainly utilized as an iron core of a transformer and required to exhibit excellent magnetization characteristics, e.g. low iron loss in particular. In this regard, it is important to highly accord secondary recrystallized grains of a steel sheet with (110)[001] orientation, i.e. what is called “Goss orientation”, and reduce impurities in a product steel sheet. However, there are limits on controlling crystal grain orientations and reducing impurities in view of production cost. Accordingly, there have been developed techniques for iron loss reduction, which is to apply non-uniformity (strain) to a surface of a steel sheet physically to subdivide magnetic domain width, i.e. magnetic domain refinement techniques.
For example, Japanese Patent No. 57-002252 proposes a technique of irradiating a steel sheet after final annealing with a laser to introduce high-dislocation density regions into a surface layer of the steel sheet, thereby narrowing magnetic domain widths and reducing iron loss of the steel sheet. Further, Japanese Patent No. 06-072266 proposes a technique of controlling magnetic domain widths by irradiating a steel sheet with an electron beam.